Stillgoing, in answer to your question, basically, there isn't going to be a big difference between 4 weeks and 6 weeks, so you might as well keep going.
Now, have you thought about a Dbol bridge? Or even, if you had it/could afford it, an Anavar bridge? If you're really concerned about the time it's going to take to get things back to normal after having run tren, then why not make your post-cycle recovery as far out from the cessation of the tren as possible?
If you have it, I'd also consider running your prop for 10 weeks. Maybe even lowering the dose for weeks 9-10.
Hmmm.. I'm going to have to explain myself here.. this would be a bit easier in conversation.. lol Basically, the BB community as a whole is a great community, but in general, one of extremes. All carbs, no carbs, all taper-cycles, no-taper-cycles, etc. I don't believe that tapering is going to get your body to start making any test, yes, as long as there's exogenous test, and you're already shut down, you'll stay shut down. However, your muscle growth is based on, and used to a certain amount of test, e.g. 500-750mg/wk. If you go from 750mg/wk to 0mg/wk, that's going to be quite a shock to the system in terms of overall strength and ability to keep it, even if you get your nuts back in a day, that's only ~150mg/wk. Why not lower your dose for a few weeks to 250mg/wk and see if you can get your body accustomed to maintaining its current size/strength at that dose, and then come down a bit further. You can see where long, or "never-ending" cycles start to make a lot of sense, and a lot of gains, when done properly. There are some people implementing this basic method already, and don't even really realize they're doing it. That's basically why I'd run an extra couple weeks of prop, to help solidify your gains. You'll also be pushing your recovery back 2 more weeks, and giving your system more time to adjust from being "shut down" by the tren.
To tren and deca. Personally, I've never experienced greater "shut down" from either of these than any other anabolics. The difference is that they decrease libido while test and other anabolics increase libido. I think this is where a certain misconception or misperception of being shut down arises. I could be wrong, but I haven't seen anything that shows that tren or nandrolone shut you down "more" than anything else. I don't even see how this is possible. Either your body is producing its own testosterone, or it's not.
The rest of your recovery, etc., I think is easily addressed by a lot of other very knowledgeable board members, I'm just offering you a few things to think about.
-B